The present invention relates to a dynamic data-rate adaptive signal processing method for transferring data signals with a predetermined signal power in a wireless infra-red data transfer system comprising an undirected, bidirectionally operable optical transfer channel involving infra-red light with a predetermined frequency between an stationary transmitter and a mobile receiver in an interior room
The advantages offered by infra-red transfer—a very large, free and available bandwidth, no interfering superposition with radio systems, utilization of the same operating frequencies in adjacent transmission systems, high data security, defined limitation of the data transfer by walls—make it a useable and attractive technology for interior communication, such as in offices, hospitals or airplanes
In the research field of wireless undirected infra-red indoors communication known systems achieve high data rates by angularly or spatially directed diversity. Optical diversity systems known from the prior art, however, require relatively complex optical systems (angularly diverse receivers or multi-beam transmitters or both). Thus, electronic signal processing methods used for improving radio systems are reasonable in infra-red transfer. However, since these two media comprise fundamentally different properties, a simple application of the known radio channel techniques for the infra-red channel cannot be carried out, but requires an investigation of its own. Due to the high dynamics with regard to bandwidth and power of the transfer response of the infra-red channel, which primarily depends upon the quality of the line of sight (LOS) between transmitter and receiver, it is difficult to achieve a good signal-noise-ratio for high data rates while using appropriate data signal power. In order to ensure user utilization and user mobility without signal interruptions, the known infra-red systems are statically configured in such a way that a reliable signal propagation is achieved indoors. The system is thereby configured for the worst propagation case. This, however, leaves a high amount of channel capacity available under good transfer conditions unused. However, in order to maximize the system data rate while at the same time ensuring secure transfer and full room coverage, the transfer system has to be configured adaptively with regard to the data transfer rate, i.e. it has to be dynamized. If the transfer channel behaviour is known, this allows for a reduction of the transfer rate under disadvantageous conditions until a predetermined error probability is reached. In adaptive signal processing, data are processes and transferred with reference to time or frequency based on a channel estimate. The current channel properties are returned from the receiver to the transmitter according to the time or frequency reference via a backchannel, where they are integrated into the adaptive signal processing. An adaptive system thus represents a closed control loop and results in an automatic adjustment of the data transfer rate in the time or frequency range depending on the current transfer quality within the channel. By configuring the system for the current channel state and not for the worst channel state, a considerably higher data rate and improved utilization of the signal power may be achieved.